Transparent pane having an electrical heating layer, method for its production, and its use

ABSTRACT

A transparent pane, having at least one heatable, electrically conductive coating connected to at least two collection electrodes, provided for electrically connecting to a supply voltage to generate a heating current that flows across a heating field formed between the at least two collection electrodes is described. The heating field includes at least one communication window free from the heatable, electrically conductive coating. The transparent pane further includes at least one heatable, electrically conductive coating. The additional electrode is connected to one of the two collection electrodes via a respective current supply line.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national stage entry ofInternational Patent Application No. PCT/EP2015/064482, filedinternationally on Jun. 26, 2015, which, in turn, claims priority toEuropean Patent Application No. 14180358.5, filed on Aug. 8, 2014.

The present invention is in the field of pane technology and relates toa transparent pane with an electrical heating layer, a method for itsproduction, as well as its use.

Transparent panes with an electrical heating layer are known per se andhave already been frequently described in the patent literature.Reference is made merely by way of example in this regard to the Germanpublished patent applications DE 102008018147 A1 and DE 102008020986 A1.In motor vehicles, they are frequently used as windshields since, due tolegal regulations, the central field of vision must have no substantialvision restrictions. By means of the heat generated by the heatinglayer, condensed moisture, ice, and snow can be removed in a short time.

The heating current is usually introduced into the heating layer by atleast one pair of strip- or band-shaped electrodes. As collectionconductors or collection electrodes, these should, as uniformly aspossible, introduce the heating current into the heating layer anddistribute it broadly. The electrical sheet resistance of the heatinglayer is relatively high with the materials currently used in industrialseries production and can be on the order of a few ohms per unit area.In order to nevertheless obtain adequate heating power for practicalapplication, the supply voltage must be correspondingly high, but, forexample, in motor vehicles, only an on-board voltage from 12 to 24 V isstandardly available. Since the sheet resistance of the heating layerincreases with the length of the current paths of the heating current,the collection conductors of opposite polarity should have the smallestpossible distance between them. For motor vehicle windows, which areusually wider than they are high, the collection conductors areunfortunately therefore arranged along the two longer pane edges suchthat the heating current can flow over the shorter path of the paneheight. However, this design results in the fact that the region of aresting or parking position of windshield wipers provided to wipe thepane customarily lies outside the heating field such that adequateheating power is no longer available there and the wipers can freeze.

There has been no lack of attempts to solve this serious problem.

Thus, European patent application EP 0 524 527 A2 presents a windshieldprovided with an electrical heating layer, wherein two flat heatingstrips are provided as heating elements in the region of a wiper parkingzone. The heating strips are in each case electrically connected via alower collection conductor arranged adjacent the lower pane edge to onepole and via a conducting wire to the other pole of a voltage source. Itis disadvantageous in this arrangement that the lower collectionconductor is additionally loaded with the current for the two heatingstrips.

In addition, the German patent application DE 102007008833 A1 and theinternational patent application WO 2008/104728 A2 present anelectrically heatable windshield that is also heatable in the region ofa wiper storage tray. For this purpose, heating wires that are connectedto a lower collection conductor as a ground connection are provided.Independently of the pane heating in the field of vision, the heatingwires are impinged upon by a potential. With this arrangement as well,the lower collection conductor is additionally loaded with the currentfor the heating wires.

In the European patent EP 1 454 509 B1 and the American U.S. Pat. No.7,026,577 B2, a transparent pane is proposed, wherein a heatable fieldof vision is enclosed by two collection rails. Here, the field of visionis separated by one of the two collection rails and, in particular, by ade-coated region, from an additional heating region. In the additionalheating region, further current collection rails of opposite polarityare provided to heat the pane in the masked region below the field ofvision.

In the international patent application WO 2011/141487 A1, a transparentpane with a transparent heating coating which extends at least over aportion of the pane surface, in particular, across its field of vision,is proposed. The heating coating is divided by at least oneheating-coating-free zone into at least one first heating coating zoneand a second heating coating zone, wherein the two heating coating zonesare electrically connected in each case to at least two collectionconductors such that after application of a supply voltage that isprovided by a voltage source, a current flows in each case via at leastone first heating field formed by the first heating coating zone and atleast one second heating field formed by the second heating coatingzone. In the coating-free zone, at least one heating element isarranged, which has an ohmic resistance such that by application of thesupply voltage to the heating element, the pane is heatable in a surfaceregion containing the heating-coating-free zone. Here, the at least oneheating element is implemented such that by application of the supplyvoltage to the heating element, the pane is heatable in at least onesurface region adjacent the coating-free zone that contains at least oneof the collection conductors.

And, not least, in the international patent application WO 2012/110381A1, a transparent pane with an electrical heating layer, which extendsover at least a portion of the pane surface and is electricallyconnectable by connection means to a voltage source, is proposed. Here,the connection means comprise a band-shaped first collection conductorand a band-shaped second collection conductor, which are, in each case,electrically conductively connected over the complete band lengthdirectly to the heating layer such that after application of the supplyvoltage, a heating current flows via a heating field formed by theheating layer. Here, the first collection conductor is directlyconnected electrically conductively to at least one first ribbonconductor; and the second collection conductor, to at least one ribbonconductor. In addition, the pane has at least one heating-field-freepane zone in which at least one electrical zone heating element isarranged. The zone heating element has an ohmic resistance such that byapplication of the supply voltage, the heating-field-free pane zone isheatable, with the zone heating element in parallel electricalconnection to the heating field directly connected electricallyconductively to the at least one first ribbon conductor and to the atleast one second ribbon conductor.

To be sure, in particular, the heatable, transparent panes of theinternational patent applications WO 2011/141487 A1 and WO 2012/110381A1 have brought certain progress; however, the increased demands of themarket require further improvements of the panes known to date.

Thus, due to the geometry in the region of the resting or parkingposition of windshield wipers, the design of the pane according to theinternational patent application WO 2011/141487 A1 can be used only in afew automobile models. Moreover, in light of the variation of the supplyvoltage and the adaptation to different ohmic resistances of the heatinglayer, the design is not flexible enough to meet all the requirements.

The heatable, transparent pane of the international patent applicationWO 2012/110381 A1 has the disadvantages that an additional process stepis required to apply the heating wires on the adhesive film made, forexample, of polyvinyl butyral (PVB). Due to this additional processstep, the adhesive film must be handled prior to lamination, whichentails a higher rate of defects because of impurities and thus a higherreject rate.

A heatable glass that prevents condensation of water is known from theEuropean patent EP 1 626 940 B1. The glass comprises, at least on one ofits sides, a resistance layer or heating layer that includes a pluralityof etchings/removals such than the glass obtains a predetermined desiredelectrical resistance. Here, the resistance layer or heating layer issubdivided by the etchings/removals into a plurality of regionsconnected to one another. In addition, the etchings/removals can be ofthe type that they form, in each case, regions of different geometriccharacteristics that, as a result, have different resistances and,consequently, different heating effects. The etchings/removals can beformed using laser technology or by grinding. The glasses are usedprimarily in freezers, as are customarily used in bars, confectionershops, or supermarkets. Here, it is disadvantageous that the resistancelayer or heating layer must be arranged between at least two busbars orcollection conductors such that only very little or no heating power ispresent outside the resistance layer or heating layer. Whether or notthis heatable glass is suitable as heating for the region of the restingor parking position of windshield wipers cannot be determined from theEuropean patent. Besides that, the course of the current path cannot beclearly discerned from FIG. 3 of the European patent because the twolonger busbars opposite one another are also separated byetchings/removals into two regions electrically isolated from oneanother. From the documents WO 2011/141487 A1, WO 03/051088 A2, U.S.Pat. No. 5,877,473 A, and EP 0 524 537 A2, other windshields withelectrically heatable coatings and special measures for wiper fieldheating are known.

In contrast, the object of the present invention consists inadvantageously improving the previously known, heatable, transparentpanes having an electrical heating layer and heating of the region ofthe resting or parking position of windshield wipers (hereinafterreferred to as “wiper parking zone”). The improved, heatable,transparent panes should have heating of the region of the wiper parkingzone that can be produced at low cost, with their design being readilyadaptable to different ohmic resistances of the electrical heating layerand different supply voltage levels.

These and other objects are accomplished according to the proposal ofthe invention by a heatable, transparent pane with the characteristicsof the independent patent claim. Further advantageous embodiments of theinvention are indicated by the characteristics of the subclaims.

In an advantageous embodiment of the pane according to the invention,the surface of the first pane, on which the electrically heatablecoating is arranged, is areally bonded to a second pane via athermoplastic intermediate layer.

As the first and, optionally, the second pane, all electricallyinsulating substrates that are thermally and chemically stable as wellas dimensionally stable under the conditions of the production and useof the pane according to the invention are, in principle, suitable.

The first pane and/or the second pane preferably contain glass,particularly preferably flat glass, float glass, quartz glass,borosilicate glass, soda lime glass, or clear plastics, preferably rigidclear plastics, in particular polyethylene, polypropylene,polycarbonate, polymethylmethacrylate, polystyrene, polyamide,polyester, polyvinyl chloride, and/or mixtures thereof. The first paneand/or the second pane are preferably transparent, in particular for theuse of the pane as a windshield or rear window of a motor vehicle orother uses in which high light transmittance is desired. In the contextof the invention, “transparent” means a pane that has transmittance >70%in the visible spectral range. For panes that are not in thetraffic-relevant field of vision of the driver, for example, for roofpanels, the transmittance can, however, also be much lower, for example,>5%.

The thickness of the pane according to the invention can vary widely andthus be eminently adapted to the requirements of the individual case.Preferably, panes with the standard thicknesses of 1.0 mm to 25 mm,preferably of 1.4 mm to 2.5 mm for motor vehicle glass and preferably of4 mm to 25 mm for furniture, appliances, and buildings, in particularfor electric heaters, are used. The size of the pane can vary widely andis governed by the size of the use according to the invention. The firstpane and, optionally, the second pane have, for example, in theautomotive industry and architectural sector, usual areas of 200 cm² upto 20 m².

The pane according to the invention can have any three-dimensionalshape. Preferably, the three-dimensional shape has no shadow zones suchthat it can, for example, be coated by cathodic sputtering. Preferably,the substrates are planar or slightly or greatly curved in one or aplurality of spatial directions. In particular, planar substrates areused. The panes can be colorless or colored.

Multiple panes are bonded to one another via at least one intermediatelayer. The intermediate layer preferably contains at least onethermoplastic plastic, preferably polyvinyl butyral (PVB), ethylenevinyl acetate (EVA), and/or polyethylene terephthalate (PET). Thethermoplastic intermediate layer can, however, also contain, forexample, polyurethane (PU), polypropylene (PP), polyacrylate,polyethylene (PE), polycarbonate (PC), polymethylmethacrylate,polyvinylchloride, poly acetate resin, casting resins, fluorinatedethylene propylene copolymers, polyvinyl fluoride, and/or ethylenetetrachloroethylene copolymers, and/or copolymers or mixtures thereof.The thermoplastic intermediate layer can be formed by one or even by aplurality of thermoplastic films arranged one above another, wherein thethickness of one thermoplastic film is preferably from 0.25 mm to 1 mm,typically 0.38 mm or 0.76 mm.

In a composite pane according to the invention composed of a first pane,an intermediate layer, and a second pane, the electrically heatablecoating can be applied directly onto the first pane or onto a carrierfilm or onto the intermediate layer itself. The first pane and thesecond pane have, in each case, an inside surface and an outsidesurface. The inside surfaces of the first and second pane are turnedtoward one another and bonded to one another via the thermoplasticintermediate layer. The outside surfaces of the first and second paneare turned away from one another and from the thermoplastic intermediatelayer. The electrically conductive coating is applied onto the insidesurface of the first pane. Of course, another electrically conductivecoating can also be applied onto the inside surface of the second pane.Even the outside surfaces of the panes can have coatings. The terms“first pane” and “second pane” are selected to distinguish between thetwo panes in a composite pane according to the invention. No informationconcerning the geometric arrangement is associated with the terms. Ifthe pane according to the invention is provided, for example, in anopening, for example, of a motor vehicle or of a building, to separatethe interior from the external environment, the first pane can face theinterior or the external environment.

The transparent pane according to the invention comprises anelectrically conductive, heatable, transparent coating that extends atleast over a substantial portion of the pane surface, in particular,over its field of vision. The electrically conductive coating iselectrically connected to at least two, in particular, two, collectionelectrodes for electrically connecting to the two poles of a voltagesource such that by application of a supply voltage, a heating currentflows via a heating field formed between the two collection electrodes.Typically, the two collection electrodes are implemented in each case inthe shape of a strip- or band-shaped electrode or collection rail or busbar for the introduction and broad distribution of the current in theconductive coating. For this purpose, they are galvanically connected tothe heating layer.

At least one, in particular, one, of the two collection electrodes, inparticular, the upper collection electrode in the installed state of thetransparent pane, can be subdivided into at least two, in particular,two, subregions separated from one another.

In an advantageous embodiment, the collection electrode is implementedas a printed-on and fired conductive structure. The printed-oncollection electrode preferably contains at least one metal, a metalalloy, a metal compound, and/or carbon, particularly preferably a noblemetal and, in particular, silver. The printing paste for producing thecollection electrode preferably contains metal particles and/or carbonand, in particular, noble metal particles such as silver particles. Theelectrical conductivity is preferably achieved by means of theelectrically conducting particles. The particles can be situated in anorganic and/or inorganic matrix such as pastes or inks, preferably asprinting paste with glass frits.

The layer thickness of the printed-on collection electrode is preferablyfrom 5 μm to 40 μm, particularly preferably from 8 μm to 20 μm, and mostparticularly preferably from 8 μm to 12 μm. Printed-on collectionelectrodes with these thicknesses are technically easy to realize andhave advantageous current carrying capacity.

The specific resistance ρ_(a) of the collection electrode is preferablyfrom 0.8 μohm·cm to 7.0 μohm·cm and particularly preferably from 1.0μohm·cm to 2.5 μohm·cm. Collection electrodes with specific resistancesin this range are technically easy to realize and have advantageouscurrent carrying capacity.

Alternatively, the collection electrode can, however, also beimplemented as a strip or in the case of a collection electrodesubdivided into subregions as at least two, in particular, two, stripsof an electrically conductive film. The collection electrode thenincludes, for example, at least aluminum, copper, tinned copper, gold,silver, zinc, tungsten, and/or tin or alloys thereof. The strippreferably has a thickness from 10 μm to 500 μm, particularly preferablyfrom 30 μm to 300 μm. Collection electrodes made of electricallyconductive foils with these thicknesses are technically easy to realizeand have advantageous current carrying capacity. The strips can beelectrically conductively connected to the electrically conductivestructure, for example, via a soldering compound, via an electricallyconductive adhesive, or by direct placement.

The electrically conductive coating of the pane according to theinvention can be subdivided into a heating field, i.e., the heatableportion of the electrically conductive coating that is situated betweenthe two collection electrodes such that a heating current can beintroduced, and a region outside the heating field mentioned.

Electrically heatable coatings are known, for example, from DE 20 2008017 611 U1, EP 0 847 965 B1, or WO2012/052315 A1. They typically includeone functional layer or a plurality, for example, two, three, or fourelectrically conductive functional layers. The functional layerspreferably include at least one metal, for example, silver, gold,copper, nickel, and/or chromium, or a metal alloy. The functional layersparticularly preferably include at least 90 wt.-% of the metal, inparticular, at least 99.9 wt.-% of the metal. The functional layers canbe made of the metal or the metal alloy. The functional layersparticularly preferably include silver or a silver-containing alloy.Such functional layers have particularly advantageous electricalconductivity with simultaneously high transmittance in the visiblespectral range. The thickness of the functional layer is preferably from5 nm to 50 nm, particularly preferably from 8 nm to 25 nm. In this rangefor the thickness of the functional layer, advantageously hightransmittance in the visible spectral range and particularlyadvantageous electrical conductivity are obtained.

Typically, at least one dielectric layer is arranged in each casebetween two adjacent functional layers of the electrically conductivecoating. Preferably, another dielectric layer is arranged below thefirst and/or above the last functional layer. A dielectric layerincludes at least one individual layer made of a dielectric material,for example, a nitride such as silicon nitride or an oxide such asaluminum oxide. The dielectric layer can, however, also comprisemultiple individual layers, for example, individual layers of adielectric material, smoothing layers, adaptation layers, blockerlayers, and/or antireflection layers. The thickness of a dielectriclayer is, for example, from 10 nm to 200 nm.

This layer structure is generally obtained by a succession of depositionprocedures that are performed by a vacuum method such as magneticallyenhanced cathodic sputtering.

Other suitable electrically conductive coatings preferably includeindium tin oxide (ITO), fluorine-doped tin oxide (SnO₂:F), oraluminum-doped zinc oxide (ZnO:Al).

The electrically conductive coating can, in principle, be any coatingthat is intended to be electrically contacted. If the pane according tothe invention is intended to enable vision through it, as is, forexample, the case with panes in the window sector, the electricallyconductive coating is preferably transparent. The electricallyconductive coating is preferably transparent to electromagneticradiation, particularly preferably to electromagnetic radiation of awavelength from 300 to 1300 nm and, in particular, for visible light.

In an advantageous embodiment, the electrically conductive coating is alayer or a layer structure of a plurality of individual layers with atotal thickness less than or equal to 2 μm, particularly preferably lessthan or equal to 1 μm.

One advantageous electrically conductive coating has a sheet resistancefrom 0.4Ω/□ to 10Ω/□. In a particularly preferred embodiment, theelectrically conductive coating according to the invention has a sheetresistance from 0.5Ω/□ to 1Ω/□. Coatings with such sheet resistances areparticularly suited for heating motor vehicle window panes with typicalonboard voltages of 12 V to 48 V or in electric vehicles with typicalonboard voltages of up to 500 V.

The electrically conductive coating can extend over the entire surfaceof the first pane. Alternatively, however, the electrically conductivecoating can extend only over a portion of the surface of the pane. Theelectrically conductive coating preferably extends over at least 50%,particularly preferably over at least 70%, and most particularlypreferably over at least 90% of the inside surface of the first pane.

In an advantageous embodiment of a transparent pane according to theinvention as a composite pane, the inside surface of the first pane hasa peripheral edge region with a width from 2 mm to 50 mm, preferablyfrom 5 mm to 20 mm, that is not provided with the electricallyconductive coating. The electrically conductive coating then has nocontact with the atmosphere and, in the interior of the pane, isprotected by the thermoplastic intermediate layer against damage andcorrosion.

In the transparent pane according to the invention, the heating fieldincludes at least one coating-free zone in which no electricallyconductive coating is present. The coating-free zone is bounded by azone edge formed, at least in sections, by the electrically conductivecoating.

In particular, the coating-free zone has a peripheral zone edge that iscompletely formed by the electrically conductive coating.

However, the zone edge can transition into the peripheral coating edgeof the electrically conductive coating such that the coating-free zoneis directly connected to the coating-free edge strip of the transparentpane according to the invention surrounding the pane edges.

The coating-free zone can have a wide variety of outlines. Thus, theoutline can be square, rectangular, trapezoidal, triangular, pentagonal,hexagonal, heptagonal, or octagonal with rounded corners and/or curvededges as well as circular, oval, drop-shaped, or elliptical. Theoutlines can have a rectilinear, wave-shaped, zigzag, and/orsawtooth-shaped course. A plurality of these geometric characteristicscan be implemented in one and the same coating-free zone.

In particular, the coating-free zone serves as a communication windowthat is permeable to electromagnetic radiation, in particular, IRradiation, radar radiation, and/or radio radiation. In addition,sensors, for example, rain sensors, can also be placed in thecommunication window.

The coating-free zone can, for example, be produced by masking duringthe application of the heating layer on a substrate or by removal of theheating layer, for example, by mechanical and/or chemical removal and/orby removal by irradiation with electromagnetic radiation, in particularlaser light irradiation, after application of the electrically heatablecoating.

In a preferred embodiment, at least one coating-free zone is present.Preferably, at least two and in particular at least three coating-freezones are present.

Preferably, the at least one coating-free zone or the at least onecommunication window is arranged in the installed state of thetransparent pane in its upper region.

The collection electrodes and/or their subregions are electricallycontacted by one or a plurality of supply lines.

The supply line is preferably implemented as a flexible film conductoror flat conductor or ribbon cable. This means an electrical conductorwhose width is clearly greater than its thickness. Such a flat conductoris, for example, a strip or a band, including or made of copper, tinnedcopper, aluminum, silver, gold, or alloys thereof. The flat conductorhas, for example, a width of 2 mm to 16 mm and a thickness of 0.03 mm to0.1 mm. The flat conductor can have an insulating, preferably polymericsheath, for example, based on polyimide. Flat conductors that aresuitable for the contacting of electrically conductive coatings in paneshave a total thickness of, for example, only 0.3 mm. Such thin flatconductors can be embedded without difficulty between the individualpanes in the thermoplastic intermediate layer. A plurality of conductivelayers electrically isolated from one another can be situated in aribbon cable.

Alternatively, thin metal wires can also be used as the electricalsupply line. The metal wires include, in particular, copper, tungsten,gold, silver, or aluminum or alloys of at least two of these metals. Thealloys can also include molybdenum, rhenium, osmium, iridium, palladium,or platinum.

In a preferred embodiment of the transparent pane according to theinvention, each of the at least two, in particular, two, collectionelectrodes is electrically conductively connected by a flat conductor ineach case to the poles of the voltage source.

In another preferred embodiment, the at least two, in particular, two,subregions of the at least one, in particular, one, collection electrodeare electrically conductively connected in each case to a flat conductorconnected to a voltage source. Preferably, the flat conductors arearranged in the region of the subregions that is near the respectiveassociated second side of the pane edge. In this embodiment, theelectrical isolation of the flat conductors from the power supply linesis done by spatial separation of the components.

In yet another preferred embodiment, the at least two, in particular,two, subregions of the at least one, in particular, one, collectionelectrode are electrically conductively connected to a flat conductor.Preferably, in this embodiment, the flat conductor is arranged centrallybetween the two opposing ends of the subregions. Preferably, this isaccomplished by a common electrically conductive connecting part or bytwo electrically conductive connecting parts associated with therespective subregion. The flat conductor can be connected to theelectrically conductive connecting part by a flat metal strip, inparticular, a copper strip.

Here, the flat conductor and the at least one connecting part as wellas, optionally, the flat metal strip, in particular a copper strip, arearranged electrically isolated from the at least two power supply lines.

In this case, the electrical isolation between the flat conductor andthe connecting part on the one hand and the at least two power supplylines on the other is accomplished by means of an electrically isolatinglayer, in particular by means of a strip-shaped, electrically isolatinglayer, between the flat conductor and the connecting part on the onehand and the at least two power supply lines on the other hand. Theelectrically isolating layer, in particular the strip-shaped,electrically isolating layer, covers at least the points of intersectionof the connecting part with the at least two power supply lines. It can,however, also abut the two end edges of the subregions opposite oneanother.

Preferably, this arrangement has as a whole a layered structure composedof the following layers positioned one over another:

-   -   a pane,    -   sections of the power supply lines covered by the insulation,    -   subregions of the coating adjacent the power supply lines        outside the heating field, on whose zone edges the edges of the        electrically isolating layer opposite one another abut; likewise        these edges can abut the end edges of the two subregions of the        collection electrode opposite one another    -   a flat conductor resting on the electrically isolating layer    -   subregions of the collection electrode, as well as    -   the connecting part electrically connected thereto.

A substantial advantage of this arrangement is that only one additionalflat conductor is required for supplying two subregions of onecollection electrode, which substantially simplifies the production ofthe transparent pane according to the invention.

For the transparent pane according to the invention, it is essentialthat it has, outside the heating field and spatially separated therefromby at least one, in particular, one, of the above described collectionelectrodes along at least one, in particular, one, first side of thepane edge, at least one further, in particular, one, heatable,electrically conductive coating of the above described type. Preferably,this further heatable, electrically conductive coating is arranged, inthe installed state of the pane according to the invention, below thelower collection electrode and/or above the upper collection electrodein the region of the wiper parking zone.

In this further heatable, electrically conductive coating, in the regionof the two second sides of the pane edge, at least one additionalelectrode is in each case arranged. Preferably, these at least twoadditional electrodes are, in the installed state of the pane accordingto the invention, aligned vertically. They are, in each case, connectedvia at least one, in particular, one, power supply line to a collectionelectrode, which has a polarity opposite the nearest collectionelectrode. This means that when the upper collection electrode iselectrically connected to the positively charged pole of a voltagesource, the two additional electrodes located above the upper collectionelectrode are electrically connected via the power supply lines to thenegatively charged lower collection electrode. If, on the other hand,the additional electrodes are arranged in the lower further heatable,electrically conductive coating below the, for example, negativelycharged lower collection electrode, they are electrically connected viathe power supply lines to the positively charged upper collectionelectrode. The person skilled in the art can readily specify otherconfigurations based on this technical teaching.

Preferably, the additional electrodes and the power supply lines arevery much longer than they are wide. The length depends mainly on thesize of the pane according to the invention. Preferably, the width isfrom 10 μm to 10 mm, in particular 10 μm to 1 mm. Preferably, they havethe same thickness as the collection electrodes.

Particularly preferably, the power supply lines have a constantthickness and width over their entire length.

The power supply lines extend along the respective associated coatingedge and along the two second sides of the pane edge, at least insections

-   -   in the associated edge strip,    -   on the associated subsection of the peripheral coating edge        electrically decoupled from the heating field by, in each case,        at least one associated coating-free line, and/or    -   in and/or on the respective associated electrically conductive        coating outside the heating field electrically decoupled from        the heating field by, in each case, at least one associated        coating-free line.

Preferably, the power supply lines run, in each case, on the associatedelectrically conductive coating outside the heating field.

Preferably, the power supply lines are, at least in sections, straight,wave-shaped, meander-shaped, sawtooth-shaped, and/or zigzag-shaped.Preferably, the power supply lines run in a straight line over theirentire length.

The pane according to the invention has, in at least one, in particularone, further heatable, electrically conductive coating at least one, inparticular at least two, counter electrode(s) associated with therespective additional electrode and electrically coupled to theassociated collection electrode of opposite polarity. In the context ofthe invention, the term “coupled” is to be interpreted as “electricallyconnected via the electrically conductive coating”.

Preferably, the additional electrodes opposite one another and thecounter electrode opposite one another are arranged as a mirror imagerelative to the centerline or axis of symmetry of the pane according tothe invention.

The pane according to the invention also has, in at least one, inparticular, one, further heatable, electrically conductive coating, atleast two, in particular, two, systems of, in each case, at least four,preferably at least five coating-free lines, which systems are arrangedas a mirror image (in particular as a mirror image relative to thevertical centerline and axis of symmetry of the transparent pane)relative to one another, which are arranged such that they direct theheating current, flowing upon application of a supply voltage from theat least two additional electrodes via, in each case, at least one,preferably at least two, counter electrode(s) associated in each casetherewith, to the at least one collection electrode of the respectiveopposite polarity, with the coating-free lines defining the currentpaths an and their length.

The additional electrode is connected directly to a collection rail viathe power supply line. In contrast thereto, the counter electrode is notdirectly connected to the other collection rail of opposite polarity.The so-called “counter electrode” is, consequently, actually not anelectrode in the actual sense, but rather a connection conductor thatconnects to one another two coating segments that are formed by thecoating-free lines such that a current can flow between the coatingsegments.

The current flow of all current paths a₁-a_(n) is driven by thedifference in potential between the additional electrode (connected tothe first collection rail) and the second collection rail. Thesegmentation of the conductive coating formed by the coating-free linesas well as the connection of the segments by means of the counterelectrode(s)/connection conductors serve to direct the current flow inthe form of the current paths a₁-a_(n).

According to the invention, the equation I applies to the current pathsa_(n) in a system of coating-free lines:VH ₁ =h ₁ :b _(n)=0.5 to 2.0, preferably 0.75 to 1.5 and, in particular,0.8 to 1.2  (I),where VH₁ represents the mathematical relationship (h₁:b_(n)), nrepresents a whole number from 2 to 30, preferably 2 to 25 and, inparticular, 3 to 20. h₁ represents the height of the current path a₁,b_(n) represents the width of a current path a_(n).

The height h₁ of the current path a₁ is the imaginary stretch that isarranged vertically relative to the flow direction of the currentbetween two adjacent coating-free lines.

a₁ is the current path from the additional electrode all the way to thenearest opposing section of the counter electrode (connectionconductor). a₂ to a_(n) designate the other current paths. The termsa₁-a_(n) can refer to the current paths themselves or, also, to thelength thereof.

The width b_(n) of a current path a_(n) is the imaginary stretch that isarranged vertically relative to the flow direction of the currentbetween two adjacent coating-free lines.

Preferably, the widths b_(n) are arranged parallel or roughly parallelto one another, preferably at an imaginary angle of ±30°, preferably±20°, and, in particular, ±10°.

The relationships of the lengths of the individual current paths a₁ toa_(n) has no effects on the specific heating power in these current pathsections. The specific heating power is influenced only by the totallength, in other words, by the total resistance of the current paths(a₁+a₂+a₃+ . . . a_(n)) as well as by the relationship VH₁ of the widthof the sections.

The coating-free lines run, at least in sections, continuously and/or asbroken lines of discrete cuts. Preferably, they run continuously intheir entire length, i.e., without cuts.

The length of the coating-free lines can vary widely and, consequently,be advantageously adapted to the requirements of the individual case.The width of the coating-free lines is very much less than their lengthand can vary in their course. Preferably, the width is constant over theentire course. Preferably, the width is in the range from 10 μm to 1 mm.

By means of this system of at least four coating-free lines, at leasttwo current paths a_(n) are defined in the relevant lower and/or upper,in particular, the lower additional heatable, electrically conductivecoating(s). Upon application of a supply voltage, the heating currentflows in the system from the at least one additional electrode via theat least one counter electrode (connection conductor) via the currentpaths to the lower and/or upper collection electrode(s).

Here, it is a very particular advantage of the system according to theinvention that by this means the lower and/or upper additional,heatable, electrically conductive coating(s) is or are heated uniformly,with the specific heating power at 300 to 900 W/m² and preferably at 350to 800 W/m².

Another particular advantage of the configuration comprising additionalelectrodes, counter electrodes (collection conductors), and systems ofcoating-free lines is that the entire configuration can be adaptedsimply, for example, by simple parallel shifts of the additionalelectrodes and/or of the counter electrode (collection conductor), tothe requirements of the individual case without the specific heatingpower adversely changing—for example, through the occurrence of hotspots and/or cold spots. The optimum configuration for the individualcase can be determined in a simple manner using customary, knownsimulation programs.

Overall, the configuration of the pane according to the invention veryeffectively prevents resting windshield wipers from freezing in thewiper parking zone even with particularly low temperatures <0° C., inparticular <−10° C.

In a preferred embodiment of the transparent pane according to theinvention, the regions in which the collection electrodes, the flatconductor(s), the additional electrode or the additional electrodes, thepower supply lines as well as the system of the coating-free lines arearranged partially or completely masked by customary, known, visuallyconcealing, opaque or non-transparent masking strips. The masking striphides these and other functional elements in these regions and alsoprotects them against UV radiation, which can damage the functionalelements. Specifically, the black masking strip includes a visuallyconcealing, opaque subregion that transitions at its edge into thevisually partially transparent subregion. The visually partiallytransparent subregion is, for example, a dot grid. Preferably, themasking strip is applied on the inner side of the outer pane, i.e., theside turned toward the inner pane, by screen printing and fired beforethe two panes are bonded together with the adhesive layer.

Preferably, the pre-products of the masking strips are applied by screenprinting on the as yet uncoated panes after which the layers applied arefired.

The panes according to the invention can be produced in customary, knownways.

Preferably, they are produced using the method according to theinvention.

The method according to the invention comprises the following processsteps:

-   (A) Producing an electrically conductive coating;-   (B) Producing at least one coating-free communication window in the    electrically conductive coating of the heating field;-   (C) Forming    -   (c1) at least two collection electrodes connected to the two        poles of a voltage source, which collection electrodes are        electrically connected to the electrically conductive coating        such that by application of a supply voltage, a heating current        flows via a heating field situated between the two collection        electrodes, and/or    -   (c2) at least two collection electrodes connected to the two        poles of a voltage source, which collection electrodes are        electrically connected to the electrically conductive coating,        wherein at least one of the two collection electrodes is        implemented divided into at least two subregions spatially        separated from one another;-   (D) Producing    -   (d1) at least two additional electrodes opposite one another as        a mirror image relative to the centerline (and axis of symmetry)        of the transparent pane;    -   (d2) at least two counter electrodes (connection conductors)        opposite one another as a mirror image relative to the        centerline (and axis of symmetry) of the transparent pane and        electrically associated with the additional electrodes, which        are electrically coupled (i.e., electrically connected via the        electrically conductive coating) upon application of a supply        voltage to the collection electrode of opposite polarity;    -   (d3) at least two power supply lines arranged as a mirror image        of each other relative to the centerline (and axis of symmetry)        of the transparent pane connecting in each case at least one        additional electrode to at least one collection electrode or in        each case to at least one of their subregions, which supply        lines run along the respective associated coating edge and along        the two second sides of the pane edge, at least in sections        -   in the associated edge strip in each case,        -   on the associated subsection of the peripheral coating edge            electrically decoupled from the heating field by at least            one associated coating-free line in each case, and/or        -   in the associated electrical coating in each case outside            the heating field electrically decoupled by at least one            associated coating-free line in each case;-   (E) Forming    -   (e1) at least two coating-free lines running along the power        supply lines on the side of the heating field as well as    -   (e2) at least two systems of at least four coating-free lines in        each case positioned opposite one another as a mirror image,        which are arranged such that they, upon application of a supply        voltage, direct the heating current flowing from the at least        two additional electrodes via at least two current paths an to        the at least one collection electrode of opposite polarity in        each case, wherein the equation I applies for the current paths        a_(n) in the system of coating-free lines:        VH ₁ =h ₁ :b _(n)=0.5 to 2.0, preferably 0.75 to 1.5 and, in        particular, 0.8 to 1.2  (I),        -   where        -   n represents a whole number from 2 to 30, preferably 2 to 25            and, in particular, 3 to 20,        -   (a₁) designates the current path from the additional            electrode all the way to the nearest opposing section of the            counter electrode (connection conductor),        -   (h₁) represents the height of the current path a₁        -   (a₂ . . . a_(n)) designates the other current paths,        -   b_(n) represents the width of another current path a_(n),            and        -   (VH₁) represents the mathematical relationship (h₁:b_(n));-   (F) wherein the process steps (B) and (E) are performed one after    the other or simultaneously and-   (G) the process steps (C) and (D) are performed simultaneously or    one after the other as well as before or after the process steps (B)    and (E).

The relationships of the lengths of the individual current paths a₁ toa_(n) has no effects on the specific heating power in these current pathsections. The specific heating power is influenced only by the totallength, in other words, by the total resistance of the current paths(a₁+a₂+a₃+ . . . a_(n)) as well as by relationship VH₁ of the width ofthe sections.

In another preferred embodiment of the method according to theinvention, the at least four coating-free lines as well as the at leasttwo systems are produced by laser ablation of the electricallyconductive coating inside and outside the heating field.

In another preferred embodiment, the process steps (C) and (D) areperformed using screen printing.

Specifically, the application of the electrically conductive coating inprocess step (A) can be done by methods known per se, preferably bymagnetic field enhanced cathodic sputtering. This is particularlyadvantageous with regard to simple, fast, inexpensive, and uniformcoating of the first pane when the pane according to the invention isdesigned as a composite pane. The electrically conductive, heatablecoating can, however, also be applied, for example, by vapor deposition,chemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), or by wet chemical methods.

The first pane can be subjected to a temperature treatment after processstep (A). Here, the first pane is heated with the electricallyconductive coating to a temperature of at least 200° C., preferably atleast 300° C. The temperature treatment can serve for increasing thetransmittance and/or reducing the sheet resistance of the electricallyconductive coating.

The first pane can be bent after process step (A), typically at atemperature of 500° C. to 700° C. Since it is technically easier to coata flat pane, this procedure is advantageous when the first pane is to bebent. However, alternatively, the first pane can also be bent beforeprocess step (A), for example, when the electrically conductive coatingit is not suitable to withstand a bending process without damage.

The application of the collection electrodes in process step (C) and thepower supply lines in process step (E) is preferably done by printingand firing an electrically conductive paste in a screen printing methodor an inkjet method. Alternatively, the collection electrodes and thepower supply lines can be applied as strips of an electricallyconductive film on the electrically conductive coating, preferablyplaced, soldered, or glued.

In screen printing methods, the lateral shaping is done by masking ofthe fabric through which the printing paste with the metal particles ispressed. By suitable shaping of the masking, the width of the collectionelectrode can, for example, be particularly easily predefined andvaried.

The coating-free zones are produced in process step (B) preferably bymechanical removal of the heatable coating produced in process step (A).The mechanical removal can also be replaced or supplemented by treatmentwith suitable chemicals and/or by irradiation with electromagneticradiation.

An advantageous improvement of the method according to the inventioncomprises at least the following additional steps:

-   -   arranging a thermoplastic intermediate layer on the coated        surface of the first pane and arranging a second pane on the        thermoplastic intermediate layer and    -   bonding the first pane and the second pane via the thermoplastic        intermediate layer.

In these process steps, the first pane is arranged such that the one ofits surfaces that is provided with the heatable coating faces thethermoplastic intermediate layer. The surface thus becomes the innersurface of the first pane.

The thermoplastic intermediate layer can be formed by a singlethermoplastic film or even by two or more thermoplastic films that arearranged areally one over another.

The bonding of the first and the second pane is preferably done underthe action of heat, vacuum, and/or pressure. Methods known per se forproducing a pane can be used.

So-called autoclave methods can, for example, be performed at anelevated pressure of roughly 10 bar to 15 bar and temperatures from 130°C. to 145° C. for roughly 2 hours. Vacuum bag or vacuum ring methodsknown per se operate, for example, at roughly 200 mbar and 80° C. to110° C. The first pane, the thermoplastic intermediate layer, and thesecond pane can also be pressed in a calendar between at least one pairof rollers to form a pane. Systems of this type for producing panes areknown and normally have at least one heating tunnel upstream from apressing facility. The temperature during the pressing procedure is, forexample, from 40° C. to 150° C. Combinations of calendar and autoclavemethods have particularly proven their value in practice. Alternatively,vacuum laminators can be used. These consist of one or a plurality ofheatable and evacuable chambers, in which the first pane and the secondpane are laminated within, for example, roughly 60 minutes at reducedpressures of 0.01 mbar to 800 mbar and temperatures from 80° C. to 170°C.

The transparent pane according to the invention, in particular thetransparent pane produced using the method according to the invention,can be used excellently as a functional and/or decorative individualpiece and/or as a built-in part in furniture, appliances, and buildings,as well as in means of transportation for travel on land, in the air, oron water, in particular in motor vehicles, for example, as a windshield,rear window, side window, and/or glass roof. Preferably, the transparentpane according to the invention is implemented as a motor vehiclewindshield or a motor vehicle side window.

It is understood that the above mentioned characteristics and thosedetailed in the following can be used not only in the combinations andconfigurations specified, but also in other combinations andconfigurations or alone without departing from the scope of the presentinvention.

BRIEF DESCRIPTION OF THE FIGURES

The invention is now explained in detail with reference being made tothe accompanying figures. They depict in simplified, not-true-to-scalerepresentation:

FIG. 1 a plan view of a windshield 1 according to the invention insimplified representation;

FIG. 2 a view of a vertical section through a detail of the windshieldaccording to the invention of FIG. 1;

FIG. 3 a perspective view of a detail of the windshield according to theinvention of FIG. 1;

FIG. 4 a plan view of the detail B of the windshield 1 according to theinvention of FIG. 1;

FIG. 5 a plan view of the detail A from an exemplary embodiment of thewindshield 1 according to the invention of FIG. 1;

FIG. 6 a plan view of the detail A from another exemplary embodiment ofthe windshield 1 according to the invention of FIG. 1, together with theenlarged detail C;

FIG. 7 a plan view of the detail A from yet another exemplary embodimentof the windshield 1 according to the invention of FIG. 1, together withthe enlarged detail D;

FIG. 8 a plan view of the detail from yet another exemplary embodimentof the windshield 1 according to the invention.

DETAILED DESCRIPTION OF THE FIGURES

FIG. 1 in Conjunction with FIGS. 2, 3, and 4

FIG. 1 depicts a transparent windshield 1 of a motor vehicle viewed fromthe inside in a simplified representation. Here, the windshield isimplemented, for example, as a composite pane, whose structure isillustrated using the representation of a vertical section through adetail of the windshield 1 in FIG. 2 and using the perspectiverepresentation of a detail of the windshield 1 in FIG. 3.

Accordingly, the windshield 1 comprises two rigid individual panes,namely an outer pane 2 and an inner pane 3 that are firmly bonded to oneanother by a thermoplastic adhesive layer 4, here, for example,polyvinyl butyral film (PVB), an ethylene vinyl acetate film (EVA), or apolyurethane film (PU). The two individual panes 2, 3 have roughly thesame size and shape and can, for example, have a trapezoidal curvedcontour, not shown in detail in the figures. They are made, for example,of glass, also possibly being constructed from a non-glass material suchas plastic. For applications other than windshields, it would also bepossible to produce the two individual panes 2, 3 from a flexiblematerial. The contour of the windshield 1 is determined by a pane edge5, common to the two individual panes 2, 3, the windshield 1 having, atthe top and bottom, two first sides 6, 6′ positioned opposite oneanother as well as, on the left and the right, two second sides 7, 7′opposite one another.

As shown in FIGS. 2 and 3, a transparent, electrically conductivecoating 8 is deposited on the side of the inner pane 3 bonded to theadhesive layer 4. Here, the heatable, electrically conductive coating 8is, for example, applied substantially to the entire surface of theinner pane 3, with a peripheral edge strip 9 on all sides not coated,such that a coating edge 10 of the electrically conductive coating 8 isset back inwardly relative to the pane edge 5. By this means, electricalisolation of the electrically conductive coating 8 relative to theoutside is effected. Moreover, the electrically conductive coating 8 isprotected against corrosion penetrating from the pane edge 5.

The electrically conductive coating 8 comprises, in a known manner, alayer sequence (not shown) with at least one electrically heatable,metallic sublayer, preferably silver, and, optionally, other sublayerssuch as antireflective and blocker layers. Advantageously, the layersequence has high thermal stability such that it withstands thetemperatures of typically 600° C. required for bending glass paneswithout damage, but also with the possibility of providing layersequences with low thermal stability. It is equally possible for theelectrically conductive coating 8 to be applied as a metallic singlelayer. It is likewise conceivable not to apply the electricallyconductive coating 8 directly on the inner pane 3 but, instead, to applyit first on a carrier, for example, a plastic film that is subsequentlyglued to the outer and inner pane 2, 3. Alternatively, the carrier filmcan be bonded to adhesive films (e.g., PVB films) and glued as atrilayer arrangement to the inner and outer pane 2, 3. The heatable,electrically conductive coating 8 is preferably applied by sputtering ormagnetron cathodic sputtering onto the inner or outer pane 2, 3.

As shown in FIG. 1, the electrically conductive coating 8 iselectrically conductively connected adjacent the first side 6, 6′, i.e.,on the upper and lower pane edge 5, to a strip-shaped upper collectionelectrode or busbar 11 and to a strip-shaped lower collection electrode11′. The upper collection electrode 11 and the lower collectionelectrode 11′ are provided for connecting to, in each case, one pole ofa voltage source (not shown). The two collection electrodes 11, 11′ ofopposite polarity serve for uniform introduction and distribution of theheating current into the heating field 12 of the heatable coating 8situated between them. The two collection electrodes 11, 11′ are, forexample, printed onto the electrically conductive coating 8 and have, ineach case, an at least approximately rectilinear course.

The collection electrodes 11, 11′ can also, however, be subdivided, ineach case, into two subregions spatially separated from one another.

The upper collection electrode 11 in the installed state of thewindshield 1 separates the heating field 12 from the subregion 8′″ ofthe electrically conductive coating 8 running along the upper first side6 of the pane edge 5.

The lower collection electrode 11′ in the installed state of thewindshield 1 separates the heating field 12 from the subregion 8′running along the lower first side 6′. This subregion 8′ serves for theheating of the wiper parking zone. Further details of variousembodiments according to the invention emerge from details A of theFIGS. 5 to 9.

Below the upper collection electrode 11, three coating-freecommunication windows are arranged in the heating field 12 centrally asa mirror image. In other words, they are divided in half by theimaginary vertical centerline M or axis of symmetry.

Two power supply lines 15, 15′ arranged as a mirror image relative toone another run from the two ends of the upper collection electrode 11in the subregions 8″ of the coating 8 along the respective associatedsubregion of the coating edge to the additional electrodes 18, 18′opposite one another in the subregion 8′. The power supply lines 15, 15′and the additional electrodes 18, 18′ are made of the same material asthe collection electrodes 11, 11′.

The power supply lines 15, 15′ and the additional electrodes 18, 18′ areelectrically decoupled by the coating-free lines 16, 16′ associated ineach case therewith, running along the power supply lines 15, 15′ on theside of the heating field 12 from the heating field 12. The coating-freelines 16, 16′ have a width of 100 μm. They are preferably producible bylaser ablation.

The coating-free lines 16, 16′ run all the way to the upper collectionelectrode 11 and continue above the upper collection electrode 11 allthe way to the peripheral edge strip 9 and separate the subregions 8″running along the second sides 7, 7′ from the subregion 8′″ runningalong the upper first side 6 from one another. Further details emergefrom the detail B of FIG. 4.

FIG. 4 depicts the intersection 17 of the coating-free line 16 with theupper collection electrode 11. Preferably, this intersection 17 isproducible by printing, by screen printing, the upper collectionelectrode 11 over the coating-free line 16 previously produced by laserablation.

FIG. 4 further depicts the preferred configuration of the black maskingstrip 13 as it is also use in the region of the lower collectionelectrode 11′ and the regions 8″, 15, 16. The masking strip 13 concealsthe functional elements in these regions and also protects them againstUV radiation, which can damage the functional elements. Specifically,the black masking strip 13 comprises a visually concealing, opaquesubregion 13′, which transitions on its edge 13″ into the visuallypartially transparent subregion 13′″, which itself reaches to the edge13″″. The visually partially transparent subregion 13′″ is, for example,a dot grid. Preferably, the masking strip 13 is applied to the inside,i.e., the side of the outer pane 2 turned toward the inner pane 3, byscreen printing and fired prior to assembly, before the two panes 2 and3 are bonded with the adhesive layer 4.

FIG. 5 in Conjunction with FIG. 1

FIG. 5 depicts a plan view of the detail A from an exemplary embodimentof the windshield 1 of FIG. 1.

The detail A portrays only the left subregion of the coating 8′ in theregion of the wiper parking zone all the way to the centerline and axisof symmetry M. The right subregion of the coating 8′ is a mirror imageof the left subregion 8′ and, consequently, is not portrayed.

In this exemplary embodiment of FIG. 5, the coating-free line 16transitions into the system 16″ of three horizontal coating-free linesand one vertical coating-free line of a line width of 30 μm. In thissystem 16″, three horizontal coating-free lines arranged parallel to oneanother branch in the left subregion 8′ at three branching points 17″.The upper coating-free line touches the upper ends 20 of the verticallyarranged additional electrode 18 and of the vertically arranged leg ofthe counter electrode/connection conductor 19. The central coating-freeline touches the lower end 20 of the additional electrode and ends atits endpoint 21 on the vertically arranged leg of the counterelectrode/connection conductor 19. The lower coating-free line runs fromits branching point 17″ out parallel to the lower peripheral coatingedge 10 along the lower first side 6′ on the way to the imaginarycenterline M and beyond.

The upper coating-free line runs after the upper end 20 of the verticalleg of the counter electrode/connection conductor 19 vertically downwardand crosses the horizontal leg of the counter electrode/connectionconductor 19 in the intersection 17′ and continues below the horizontalleg all the way to the branching point 17″ of the lower coating-freeline.

Details of the endpoints 20 are apparent from the enlarged detail C inFIG. 6. Details of the branching points 17″ are apparent from theenlarged detail D of FIG. 7.

Two current paths a₁ and a₂ are formed in the subregion 8′ by thissystem 16″ of four coating-free lines. The current path a₁ runs from theadditional electrode 18 to the vertical leg of the counterelectrode/connection conductor 19; it is thus, in this embodiment and inthe subsequently described embodiments, the first current path. From thehorizontal leg of the counter electrode/connection conductor 19, thecurrent path a₂ runs all the way to the lower collection electrode 11′.The relationship VH₁=0.9 wir and n=2. Upon application of a supplyvoltage of 12 V, the heating current flows in the system 16″ from theadditional electrode 18 via the counter electrode/connection conductor19 to the lower collection electrode 11′.

It is a very particular advantage of the system 16″, 18, 19 according tothe invention that by means of it the coating 8′ is heated uniformly,the specific heating power being at 400 to 550 W/m². Another veryparticular advantage of the system 16″, 18, 19 according to theinvention is, furthermore, that the entire configuration can be adaptedby a simple parallel shift P, for example, of the additional electrode18 and/or of the vertical leg of the counter electrode/connectionconductor 19 to the requirements of the individual case without thespecific heating power being disadvantageously altered—for example, bythe occurrence of hot spots and/or cold spots. The optimum configurationof the electrodes 18, 19 and of the current paths a₁ . . . a_(n) can bedetermined in a simple manner for the individual case using customary,known simulation programs.

Overall, even at particularly low temperatures <0° C., the embodiment ofthe transparent pane according to the invention 1 of FIG. 5 effectivelyprevents the windshield wipers from freezing in the wiper parking zone.

FIG. 6 in Conjunction with FIG. 1

FIG. 6 depicts a plan view of the detail A from an exemplary embodimentof the windshield 1 of FIG. 1.

As in FIG. 5, the detail A portrays only the left subregion of thecoating 8′ in the region of the wiper parking zone all the way to thecenterline and axis of symmetry M. Here again, the right subregion ofthe coating 8′ is a mirror image of the left subregion 8′ and,consequently, does not need to be portrayed.

In this exemplary embodiment of FIG. 6, the coating-free line 16transitions into the system 16″ of a total of three horizontal and twovertical coating-free lines of a line width of 30 μm. In this system16″, three horizontal coating-free lines arranged parallel to oneanother branch, in the left subregion 8′, at the three branching points17″. The upper coating-free line touches the upper and of the additionalelectrode 18. For details, reference is made to the enlarged detail C ofFIG. 6. Then, the coating-free line runs along the horizontal leg of thetwo-part counter electrode/connection conductor 19. In this region, avertical coating line branches (branching point 17″), which line runsall the way to the lower horizontal coating-free line. The centerhorizontal coating-free line of the system 16″ touches the lower ends ofthe vertical additional electrode 18 and of the vertical leg of thetwo-part counter electrode/connection conductor 19 and runs all the wayto the branching point 17″ with the coating-free line arranged along thevertical leg of the counter electrode/connection conductor 19. Detailsconcerning the branching points 17″ are apparent from the detail D ofFIG. 7.

In the region of the end of the horizontal leg of the two-part counterelectrode/connection conductor 19, the coating-free line runs verticallydownward and crosses a subregion of the counter electrode/connectionconductor 19 spatially separated therefrom but electrically coupled tothe horizontal leg. The intersection 17′ has the same configuration asthe intersection 17 in FIG. 4. The subregion of the counterelectrode/connection conductor 19 is then electrically coupled to thelower collection electrode 11′, namely, via the electrically conductivecoating.

Three current paths a₁, a₂, and a₃ are formed by this system 16″ of fivecoating-free lines. The current path a₁ runs from the additionalelectrode 18 to the vertical leg of the two-part counterelectrode/connection conductor 19. The current path a₂ runs from thehorizontal leg of the counter electrode/connection conductor 19 all theway to the separate horizontal subregion of the counterelectrode/connection conductor 19. The current path a₃ runs from theseparate horizontal subregion of 19 to the lower collection electrode11′.

The additional electrode 18 is directly connected to the firstcollection rail 11 via the power supply line 15. In contrast thereto,the counter electrode 19 is not directly connected to the secondcollection rail 11′. The counter electrode 19 is a connection conductorthat connects to one another two coating segments that are formed by thecoating-free lines such that a current can flow between the coatingsegments.

The current flow of all current paths a₁-a_(n) is driven by thedifference in potential between the additional electrode 18 (connectedto the first collection rail 11) and the second collection rail 11′. Thesegmentation of the conductive coating formed by the coating-free linesas well as the connection of the segments by means of the counterelectrode(s) 19 serve to direct the current flow in the form of thecurrent paths a₁-a_(n).

The relationship VH₁=1, the relationship VH₂=1, and n=2 and 3. Uponapplication of a supply voltage of 12 V, the heating current flows inthe system 16″ from the additional electrode 18 via the counterelectrode/connection conductor 19 to the lower collection electrode 11′.Upon application of a supply voltage of 12 V, the current flows in thesystem 16″ from the additional electrode 18 via the two-part counterelectrode/connection conductor 19 to the lower collection electrode 11′.

It is a very particular advantage of this system 16″, 18, 19 accordingto the invention as well that by this means the coating 8′ is heateduniformly, with the specific heating power at 400 to 550 W/m². Anothervery particular advantage of the system 16″, 18, 19 according to theinvention is, furthermore, that the entire configuration can be adapted,by a simple parallel shift P, for example, of the additional electrode18 and/or of the vertical leg of the counter electrode/connectionconductor 19, to the requirements of the individual case without thespecific heating power adversely changing—for example, through theoccurrence of hot spots and/or cold spots. The optimum configuration ofthe electrodes 18, 19 and of the current paths a₁ . . . a_(n) for theindividual case can be determined in a simple manner using customary,known simulation programs.

Overall, the embodiment of the transparent pane 1 according to theinvention of FIG. 6 effectively prevents the windshield wipers fromfreezing in the wiper parking zone even with particularly lowtemperatures of <0° C.

FIG. 7 in Conjunction with FIG. 1

FIG. 7 depicts a plan view of the detail A from an exemplary embodimentof the windshield 1 of FIG. 1.

As in FIGS. 5 and 6, the detail A portrays only the left subregion ofthe coating 8′ in the region of the wiper parking zone all the way tothe centerline and axis of symmetry M. Here again, the right subregionof the coating 8′ is a mirror image of the left subregion 8′ and,consequently, does not need to be portrayed.

In this exemplary embodiment of FIG. 7, the coating-free line 16transitions into the system 16″ of a total of three horizontal and threevertical coating-free lines of a line width of 30 μm. In this system16″, three horizontal coating-free lines arranged parallel to oneanother branch, in the left subregion 8′, at the three branching points17″. Of these, the upper coating-free line touches the upper end of thevertical additional electrode 18 and the upper end of the vertical legof the three-part additional electrode 19. Thereafter, the uppercoating-free line runs along the spatially separate upper subregion ofthe three-part counter electrode/connection conductor 19. The uppersubregion is coupled to the lower horizontal leg of the three-partcounter electrode and its third spatially separate lower subregion.

After the endpoint 20, there is a branching 17″ where one coating-freeline branches vertically downward and runs along the vertical leg of thetwo three-part counter electrodes/connection conductors 19 (for details,cf. the enlarged detail D of FIG. 7), intersects the lower horizontalleg and ends at the lower horizontal coating-free line. In the furthercourse, the upper horizontal coating-free line branches once more,whereupon the branched coating-free line runs vertically downward,touches the endpoint 20 of the horizontal lower leg, runs furtherthrough the gap between the end of the horizontal lower leg and thethird horizontal subregion of the three-part counterelectrode/connection conductor 19, and, after that, coincides with thelower horizontal coating-free line.

The upper coating-free line runs along the horizontal upper subregion ofthe counter electrode/connection conductor 19 and, after that, bendsvertically downward, touches the end of the horizontal upper subregion,intersects at 17′ the horizontal, lower, third subregion of thethree-part counter electrode/connection conductor 19, and then alsocoincides with the lower horizontal coating-free line.

The horizontal, lower, third subregion of the three-part counterelectrode/connection conductor 19 then runs further all the way to thecenterline and axis of symmetry M.

Four current paths a₁, a₂, a₃, and a₄ are formed by this system 16″ ofsix coating-free lines. The current path a₁ runs from the additionalelectrode 18 to the vertical leg of the three-part counterelectrode/connection conductor 19. The current path a₂ runs from thehorizontal lower leg of the counter electrode 19 all the way to theseparate horizontal upper subregion of the counter electrode/connectionconductor 19. The current path a₃ runs from this separate horizontalupper subregion of 19 to the horizontal lower subregion of thethree-part counter electrode/connection conductor 19. From there out,the current path a₄ runs to the lower collection electrode 11′.

The relationship VH₁=1.5 and n=2 to 4. Upon application of a supplyvoltage of 12 V, the current flows in the system 16″ from the additionalelectrode 18 via the three-part counter electrode 19 to the lowercollection electrode 11′.

It is a very particular advantage of this system 16″, 18, 19 accordingto the invention as well that by means of it, the coating 8′ is heateduniformly, the specific heating power being at 400 to 550 W/m². Anothervery particular advantage of the system 16″, 18, 19 is, furthermore,that the entire configuration can be adapted by simple parallel shiftsP, for example, of the additional electrode 18 and/or of the verticalleg of the counter electrode/connection conductor 19 to the requirementsof the individual case, without the specific heating power beingdisadvantageously altered—for example, by the occurrence of hot spotsand/or cold spots. The configuration of the electrodes 18, 19 and of thecurrent paths a₁ . . . a_(n) optimum for the individual case can bedetermined in a simple manner using customary, known simulationprograms.

Overall, even at particularly low temperatures <0° C., the embodiment ofthe transparent pane 1 according to the invention of FIG. 7 effectivelyprevents the windshield wipers from freezing in the wiper parking zone.

FIG. 8 in Conjunction with FIG. 1

FIG. 8 depicts a plan view of the detail A from an exemplary embodimentof the windshield 1 of FIG. 1.

As in FIGS. 5, 6, and 7, the detail A portrays only the left subregionof the coating 8′ in the region of the wiper parking zone all the way tothe centerline and axis of symmetry M. Here again, the right subregionof the coating 8′ is a mirror image of the left subregion 8′ and,consequently, does not need to be portrayed.

The design of the windshield 1 of FIG. 8 is a further development of thedesign of the windshield 1 of FIG. 6. The difference resides in the factthat in the design of FIG. 8 the coating 8′ in the region of the wiperparking zone is divided by two horizontal and ten vertical coating-freelines into ten current paths a₁-a₁₀ and not into three current pathsa₁-a₃ by three horizontal and three vertical coating-free lines.

The relationship VH₁=1.5 and n=2 to 5. Upon application of a supplyvoltage of 12 V, the current flows in the system 16″ from the additionalelectrode 18 via the four-part counter electrode/connection conductor 19to the lower collection electrode 11′.

It is a very particular advantage of this system 16″, 18, 19 accordingto the invention as well that by this means the coating 8′ is heatedespecially uniformly, with the specific heating power at 500 to 700 to 0W/m². Another very particular advantage of the system 16″, 18, 19according to the invention is that the entire configuration can beadapted, by simple parallel shifts P, for example, of the additionalelectrode 18 and/or of the vertical leg of the counterelectrode/connection conductor 19, to the requirements of the individualcase without the specific heating power adversely changing—for example,through the occurrence of hot spots and/or cold spots. The optimumconfiguration of the electrodes 18, 19 and of the current paths a₁ . . .a_(n) for the individual case can be determined in a simple manner usingcustomary, known simulation programs.

Overall, the embodiment of the transparent pane 1 according to theinvention of FIG. 7 effectively prevents the windshield wipers fromfreezing in the wiper parking zone, even with particularly lowtemperatures of <0° C.

In FIGS. 1 to 8, the reference characters have the following meaning:

-   1 windshield-   2 outer pane-   3 inner pane-   4 adhesive layer-   5 peripheral pane edge-   6, upper first side of the pane edge 5 in the installed state of the    windshield 1-   6′ lower first side of the pane edge 5 in the installed state of the    windshield 1-   7, 7′ lateral second side of the pane edge 5 in the installed state    of the windshield 1-   7 electrically conductive coating-   8′ lower electrically conductive coating 8 arranged in the region of    the wiper parking zone outside the heating field 12 along the lower    first side 6′ of the pane edge 5 in the installed state of the    windshield 1-   8″ subregions of the electrically conductive coating 8 arranged    outside the heating field 12 along the second sides 7 and 7′ of the    pane edge 5 in the installed state of the windshield 1-   8′″ subregion of the electrically conductive coating 8 arranged    outside the heating field 12 along the upper first side 6 of the    pane edge 5 in the installed state of the windshield 1-   9 peripheral edge strip free of the electrically conductive coating    8-   10 peripheral coating edge-   11, upper collection electrode in the installed state of the    windshield 1-   11′ lower collection electrode in the installed state of the    windshield 1-   12 heating field-   13 masking strip-   13′ visually concealing, opaque subregion of the masking strip 13-   13″ edge of the visually concealing, opaque subregion of the masking    strip 13-   13′″ visually partially transparent subregion of the masking strip    13-   13″″ edge of the visually partially transparent subregion of the    masking strip 13-   14 communication window free of the electrically conductive coating    8-   15, 15′ power supply lines running from the upper collection    electrode 11 along the respective associated coating edge 10 in the    respective associated subregions 8″ to the additional electrodes 18,    18′-   16, 16′ coating-free line running along the power supply lines 15,    15′ on the side of the heating field 12-   16″ system of at least four coating-free lines in the coating 8′ in    the region of the wiper parking zone-   17 intersection of the coating-free lines 16, 16′ with the    collection electrode 11-   17′ intersection of a coating-free line 16″ with a counter electrode    19-   17″ branching point of a coating-free line 16″-   18, 18′ additional electrodes electrically connected to the    collection electrode 11 via power supply lines 15, 15′ arranged in    the lower electrically conductive coating 8′ (wiper parking zone)-   19 counter electrode to the additional electrode 18 (connection    conductor)-   20 endpoint of an additional electrode 18 or a counter electrode 19    on a coating-free line 16″-   21 endpoint of a coating-free line 16″ on an additional electrode 18    or a counter electrode 19-   a₁ length of the current path from the additional electrode 18 to    the nearest opposing section of the counter electrode 19-   a₂, . . . , a_(n) length of a current path-   h₁ height of the current path a₁-   b₂, . . . b_(n) width of the current paths a₂ to a_(n)-   ½b₆ one half of the width b₆-   A enlarged detail of the windshield 1-   B enlarged detail of the windshield 1-   C enlarged detail of the windshield 1-   D enlarged detail of the windshield 1-   M vertical centerline and axis of symmetry-   P parallel shift

The invention claimed is:
 1. A transparent pane comprising: i) at leastone heatable, electrically conductive coating connected to at least twocollection electrodes adapted for electrical connection to two poles ofa voltage source so that upon application of a supply voltage, a heatingcurrent flows via a heating field formed between the at least twocollection electrodes, wherein: ia) the heating field has at least onecommunication window free of the heatable, electrically conductivecoating, and ib) the heatable, electrically conductive coating isbounded by a peripheral coating edge, and a peripheral edge strip thatis free of the electrically conductive coating and extends all the wayto a peripheral pane edge of the transparent pane, ii) two first sidesincluding a top side and a bottom side, and two second sides including aleft side and a right side, iii) at least one heatable, electricallyconductive coating arranged outside the heating field and spatiallyseparated from the heating field by a collection electrode of the atleast two collection electrodes that runs along a first side of the paneedge; and iv) at least one additional electrode arranged in a region ofeach of the two second sides of the pane edge, each connected to a firstcollection electrode of the at least two collection electrodes via atleast one power supply line that runs along the peripheral coating edgeand along a respective one of the two second sides of the pane edgethrough one or more of: iva) a section of the peripheral edge strip,ivb) a section of the peripheral coating edge that is electricallydecoupled from the heating field by a respective at least one associatedcoating free line, and ivc) a section of the heatable, electricallyconductive coating arranged outside the heating field that iselectrically decoupled from the heating field by a respective at leastone associated coating free line; wherein the heatable electricallyconductive coating arranged outside the heating field comprises: A) atleast one connection conductor electrically associated with each of theat least one additional electrode, and electrically connected to asecond collection electrode of the at least two collection electrodesvia the heatable, electrically conductive coating, the second collectionelectrode having an opposite polarity from a polarity of the firstcollection electrode, and B) at least two systems of coating-free lines,each comprising at least four coating-free lines, positioned oppositeone another as a mirror image relative to a vertical centerline and axisof symmetry of the transparent pane that are configured to direct theheating current, flowing upon application of a supply voltage, from eachof the at least one additional electrode to the second collectionelectrode of opposite polarity via: B1) at least two current pathscomprising a current path a₁ and remaining current paths a₂ to a_(n),formed in regions of the heatable, electrically conductive coatingarranged outside the heating field, and B2) the at least one connectionconductor, wherein lengths of the current paths satisfy a mathematicalrelationship VH1:VH ₁ =h ₁ /b _(n)=0.5 to 2.0, where n represents an integer number from2 to 30, a₁ designates the current path from the at least one additionalelectrode to a nearest opposing section of the at least one connectionconductor, h₁ represents a height of the current path a₁ delimited bytwo coating-free lines of the at least four coating-free lines, a₂ toa_(n) designate the remaining current paths from at least one connectionconductor to a nearest section of another connection conductor or fromthe other connection conductor to the second collection electrode, b_(n)represents a width of a current path a_(n), and VH₁ represents a ratioof the height of the current path a₁ to the width of the current patha_(n).
 2. The transparent pane according to claim 1, wherein each of theat least one additional electrode, the at least one connection conductorassociated therewith, the systems of coating-free lines, and the currentpaths a₁ and a₂ to a_(n), are arranged as a mirror image relative to thevertical centerline and axis of symmetry of the transparent pane.
 3. Thetransparent pane according to claim 1, wherein VH₁=0.75 to 1.5.
 4. Thetransparent pane according to claim 1, wherein VH₁=0.8 to 1.2.
 5. Thetransparent pane according to claim 1, wherein at least one of the atleast four coating-free lines runs, at least in sections, in one or moreof: a) rectilinearly, b) wave-shaped, c) meander-shaped, d)sawtooth-shaped, and e) zigzag-shaped.
 6. The transparent pane accordingto claim 1, wherein at least one of the at least four coating-free linesruns, at least in sections, in one or more of: a) continuously, and b)as a broken line of discrete cuts.
 7. The transparent pane according toclaim 1, wherein at least one of the at least four coating-free lines isproduced by laser ablation of the heatable, electrically conductivecoating of the heating field, of the electrically conductive coating, orof both of the electrically conductive coating of the heating field andthe electrically conductive coating.
 8. The transparent pane accordingto claim 1, wherein in the installed state of the transparent pane, theheatable, electrically conductive coating arranged outside the heatingfield is arranged along the bottom side of the pane edge.
 9. Thetransparent pane according to claim 1, wherein in the installed state ofthe transparent pane, the heatable, electrically conductive coatingarranged outside the heating field is arranged along the top side of thepane edge.
 10. The transparent pane according to claim 8, wherein theheatable, electrically conductive coating arranged outside the heatingfield is arranged in a region of a lower or of an upper wiper parkingzone.
 11. The transparent pane according to claim 1, wherein the atleast four horizontal coating-free lines have each a width of 10 pm to 1mm.
 12. The transparent pane according to claim 1, wherein at least oneof the at least two collection electrodes is divided into at least twosubregions spatially separated from one another.
 13. A method forproducing the transparent pane according to claim 1, the methodcomprising the following process steps: (A) producing the heatable,electrically conductive coating; (B) producing the at least onecoating-free communication window in the heatable, electricallyconductive coating of the heating field, said heating field being formedbetween the at least two collection electrodes; (C) forming: (c1) the atleast two collection electrodes for connection to the two poles of thevoltage source, the at least two collection electrodes beingelectrically connected to the heatable, electrically conductive coatingso that by application of the supply voltage, the heating current flowsvia the heating field, and/or (c2) the at least two collectionelectrodes for connection to the two poles of the voltage source, the atleast two collection electrodes being electrically connected to theheatable, electrically conductive coating, wherein at least one of theat least two collection electrodes is divided into at least twosubregions spatially separated from one another; (D) producing: (d1) inthe region of each of the two second sides of the pane edge, the atleast two additional electrodes opposite one another as a mirror imagerelative to the vertical centerline and axis of symmetry of thetransparent pane; (d2) at least two connection conductors as a mirrorimage opposite one another relative to the vertical centerline and axisof symmetry of the transparent pane and electrically associated with theadditional electrodes, said connection conductors being electricallyconnected, upon application of the supply voltage, to the collectionelectrode of opposite polarity via the heatable, electrically conductivecoating; and (d3) at least two power supply lines arranged as a mirrorimage of each other relative to the vertical centerline and axis ofsymmetry of the transparent pane, each of said power supply linesrespectively connecting at least one of the additional electrodes to atleast one collection electrode or subregion thereof, and running alongthe coating edge and along a respective one of the two second sides ofthe pane edge, through one or more of: the section of the peripheraledge strip, the section of the peripheral coating edge that iselectrically decoupled from the heating field by a respective at leastone associated coating-free line, and the section of the heatable,electrically conductive coating arranged outside the heating field thatis electrically decoupled from the heating field by a respective atleast one associated coating-free line; (E) forming: (e1) at least twocoating-free lines running along the power supply lines on the side ofthe heating field; (e2) the at least two systems of coating-free linespositioned opposite one another as a mirror image, each comprising atleast four coating-free lines that are arranged so that, uponapplication of the supply voltage, the heating current flows directlyfrom a respective one of the at least one additional electrode to thesecond collection electrode of opposite polarity via: at least the twocurrent paths comprising the current path a₁ and remaining current pathsa₂ to a_(n), and the at least one connection conductor, wherein thelengths of the current paths satisfy the mathematical relationship VH₁:VH ₁ =h ₁ /b _(n)=0.5 to 2.0 where n represents an integer number from 2to 30, (a₁) designates the current path from the at least one additionalelectrode to the nearest opposing section of the at least one connectionconductor, (h₁) represents the height of the current path a₁ delimitedby two coating-free lines of the at least four coating-free lines (a₂ toa_(n)) designate the remaining current paths from at least oneconnection conductor to the nearest section of another connectionconductor or from the other connection conductor to the secondcollection electrode, and bn represents the width of the current patha_(n), VH₁ represents the ratio of the height of the current path a₁ tothe width of the current path a_(n), wherein the process steps (B) and(E) are performed one after the other or simultaneously, and wherein theprocess steps (C) and (D) are performed simultaneously or one after theother as well as before or after the process steps (B) and (E).
 14. Themethod according to claim 13, wherein VH₁=0.75 to 1.5.
 15. The methodaccording to claim 14, wherein: the at least two coating-free lines andthe at least two systems of coating-free lines are produced by laserablation of the heatable, electrically conductive coating inside andoutside the heating field, and the process steps (C) and (D) areperformed using screen printing.
 16. A method, comprising using of thetransparent pane produced in accordance with the method of claim 13 as afunctional, or decorative, or both functional and decorative singlepiece and as an assembly part in furniture, appliances, buildings, andmeans of transportation.